1. Field of the Invention
The present invention relates to a polymeric polymer, particularly to a polymeric polymer containing poly(oxyethylene)-amine, and application thereof to preparing silver nanoparticles. The silver nanoparticles can be further used for manufacturing electric devices, biomedicines, silver nanowires, silver paste, composites and polymer-type surfactants.
2. Related Prior Art
So far, methods for producing silver nanoparticles are classified into physical methods and chemical methods. The physical method usually demands expensive equipment for highly-vacuum vaporization or e-beam. The chemical method uses reducers to reduce the silver ions as atoms and then a stabilizer is used to control the size of the particles. Representative reducers include NaBH4, formaldehyde, alcohol, hydrazine (H2N—NH2), and the like. Representative stabilizers include sodium citrate, glucose, sodium dodecyl sulfate, polyvinyl pyrrolidone (PVP), dendrimer, and the like.
To be applied to germproof, pharmaceutical, biomedicine and electric devices, the silver particles must have high specific area and be at nanoscale. Therefore, aggregation of the particles should be prevented, and organic dispersants or stabilizers are added to achieve this. Functions of the dispersants include electrostatic repulsion and steric hindrance or barrier, as described below.
(1) Electrostatic Repulsion
When organic dispersants are adsorbed onto the same charged surfaces of inorganic particles, Coulomb's electrostatic force will prevent the particles from aggregation. If anions on the surfaces are replaced with neutral ions, the surface charges will decrease and the particles will aggregate due to van der Waal force. In addition, high concentration or ionic strength of the prepared nanoparticle solutions often encounter the problem of lower stability, which can be overcome by using a dispersant with increased dielectric strength or electric double layers for improved stability.
(2) Steric Hindrance or Barrier
When organic molecules (serving as protectors) are adsorbed on surfaces of metal particles and prevent aggregation of the particles, steric hindrance to particle collision in rendering stability is achieved.
Some stabilizers known in the art are disclosed in reports. In J. Phys. Chem. B 1998, 102, 10663-10666, sodium polyacrylateor polyacrylamide was provided as a stabilizer. In Chem. Mater. 2005, 17, 4630-4635, thioalkylated poly(ethylene glycol) was provided as a stabilizer. In J. Phys. Chem. B1999, 103, 9533-9539, sodium citrate was provided as a stabilizer. In Langmuir 1996, 12, 3585-3589, nonionic surfactants were provided as stabilizers. In Langmuir 1997, 13, 1481-1485, NaBH4 was provided as a reducing agent and anionic, cationic and nonionic surfactant were provided as stabilizers. In Langmuir 1999, 15, 948-951, 3-aminopropyltrimethoxysilane (APS) was provided as a stabilizer and N,N-dimethyl-formamide was a reducing agent.
In addition, poly(oxyethylene) compounds (POE) can be a reducing agent of metallic ions but concentrations of the metallic ions must be low. In J. Phys. Chem. 1999, 99, 475-478, PEG having different molecular weights were discussed about their reducing ability to gold ions. The reaction formula was as follows:(AuCl4−)-PEG→Au(I)+4Cl−+2H++oxidation product3Au(I)→2Au+Au(III).
In J. Colloid Interface Sci. 2002, 255, 299-302, PEG having different molecular weights, dimethylacetamide (DMAC), acetonenitrile and water were compared about their reducing ability to silver ions and sizes of the prepared particles. In J. Phys. Chem. B 2005, 109, 7766-7777, the copolymer of poly(oxypropylene) (POP) and POE reduced gold ions into gold particles according to the following reaction:(AuCl4−)-(PEO-PPO-PEO)n→Au+4Cl−+2H++oxidation product.
As described above, the traditional method for stabilizing Ag particles is to add surfactants or stabilizers. However, the solutions of such Ag particles have solid contents less than 10% and cannot be in the form of silver paste, or have a higher solid content with aggregation.
Conventional chemical methods require the use of organic solvents, salts or reducing agents for long-term and complex redox reactions, which result in high cost. Moreover, concentrations of the silver ions have to be lowered to ppm scale during operation or the silver particles will aggregate and perform undesired effects. Accordingly, there remains a need for developing more efficient and cost effective methods for preparing silver nanoparticles.